A tuya! Click on the image to see a larger version. Image by Erik Klemetti.

Alright, well, that doesn’t entirely help, does it?

Lets look at the feature the arrow indicates. Some observations:

(1) It is low and broad.
(2) It has a relatively flat top.
(3) It is steep-sided.
(4) If you look real close, you can see crudely columnar jointing in the some of the outcrops near the top.
(5) If you had a piece of it in your hand, you’d know it was a volcano rock (andesite, very rarely you can find bits that are quite glassy).
(6)(And right next door to this feature is a reddish cone that is obviously a cinder/scoria cone.

So, what is it? How can you construct a flat-topped volcanic landforms with features that indicate a strong cooling gradient (columnar jointing, glassy material) when right next door is lava erupting to form a cinder cone?

Easy! Ice! And lots of it.

A tuya is a subglacial volcanic landform formed when there are eruptions that cannot penetrate the ice sheet above, thus forming a flat-topped hill that conforms to the bottom of the ice (after some has melted away of course). This tuya in question is found in the Central Oregon Cascades – Hayrick Butte – and it is one of a few tuya found in the High Casacades of Oregon. Much of the evidence of its subglacial origin has been removed by other erosional glacial processes, but there are still places where you can convince yourself that the columnar jointed formed by lava meeting ice are still present. The steep sides formed because the lava erupted couldn’t flow far due to the ice surrounding it. Ice-contact eruptions can form quite impressive glassy pillows – the image below is a ice-contact pillow I collected from North Sister in Oregon and the groundmass of the lava is a shiny, dark grey glass on the outer edges but much stonier in the interior, away from the direct contact with the ice. You can also find evidence for subglacial or at least ice-melt influenced explosive volcanism in the Central Oregon Cascades – this takes the form of highly altered tuff deposits on North Sister.

Ice-contact pillow collected from North Sister volcano, Oregon. Note the dark, glassy (and puffy) rind with a grey/red stony interior. The glassiness is formed by direct contact of the lava with ice. Click on the image to see a larger version. Image by Erik Klemetti.

Hayrick Butte likely formed during the height of the last ice age during the Pliocene, while the nearby Hoodoo Butte (the scoria cone) was not formed subglacially, thus its more typical cone-shaped profile. So, maybe a few thousand years separated these two volcanoes, but they ended up with very different surface expressions controlled by whether they erupted into air or underneath a kilometer-thick ice sheet. This tuya is also great evidence that there was once an ice sheet over the Central Oregon Cascades (at least locally) where today few glaciers remain.

I agree that it’s not connected… directly. But in the regard that just about every volcano in Iceland exists because of rifting, (MAR) if there is an increased incidence of rifting, then that would probably be a connection for the newly awakened volcanoes affected by it. But a conduit connecting the two? Nah, no evidence of that.

I was taught that tuyas are quite different. They begin as subglacial forms, building up steep-sided hyaloclastite piles (this is a gross simplification, though – there are really pillows and all sorts in there, all forming distinct layers), and then at some point they breach the ice surface. At this point you get lava flows across the ice surface, forming the flat ‘cap’ on the top. The two layers – hyaloclastite (and pillows, etc) and capping flow – are very distinct.

I was taught this (twice, actually, by different lecturers) at University of Iceland last year. They have more than enough tuyas to go around, so I assume they are correct!

I should add that subglacial eruptions that do NOT break the surface produce either hyaloclastite mounds (point source eruptions) or moberg ridges (fissures). At least, that’s what University of Iceland are teaching… 😉

A question for the experts: tuyas are the product of a (fairly sustained) subglacial eruption. Sustained subglacial eruptions in Iceland -and elsewhere- often generate jokulhlaups (sp?) So the question; are there any tuyas which can be linked to areas of floodwater-deposited sediments likely to be left by jokulhlaups?

I went to a talk at OSU in the late 80’s, where researcher argued that Hayrick Butte was a tuya- though I don’t think he used that word. Sitting through the discussion, I thought he made a good argument. Afterward, though, Ed Taylor made it very clear that he disagreed, saying that many of the features discussed could have been formed by “normal” volcanism. Has further research clarified the sub-glacial nature of this edifice?

according to the wikipedia article on Tuya (http://en.wikipedia.org/wiki/Tuya) the word may be derived from a Talhtan word, a first peoples nation in
British Columbia, by way of geologist Bill Mathews. Are there any other North American Indian words that have found their way into international Volcano terminology?

In the old days, people used to build their settlements at easily defended places -many of the Etruscan towns, for instance, were built on hilltops. Are there any examples of indian settlements built on tuyas? The flat area surrounded by steep sides would make an ideal natural fortress, maybe with a path to bring llamas up to browse on the plateaux during a siege.

Thuya (the Cypress family), are commonly known as ‘thujas’. A popular ornamental plant found in many gardens around the world, they’re indigenous to North America and East Asia.

In fact, Thuja plicata is the Provincial Tree of British Columbia. British Columbia and The Yukon are ‘rich’ in tuya: Tuya Volcanic Field, Tuya River, Tuya Butte and Hoodoo Mountain – a tuya, of course.

The shape of many shrub-cypress is indeed tuya-like. Makes you wonder if the latin family name was derived from the volcanic term.

The Tahltan language was spoken, not written. The People, like many aboriginal tribes of Western Canada and Alaska, were decimated by smallpox and measles epidemics concurrent with the gold mining rush of the mid Nineteenth Century.

I must agree with James (#6 and #7)…I was also taught (and have taught to MANY others, passing along knowledge I believed to be correct) that the majority of a tuya is the hyaloclastite base, which is produced by a sequence of explosions (or continuous ones) as new lava contacts ice and steam fragments it. I suppose pillows may be produced in some instances (although there would have to be enough pressure to keep the steam from blowing them up), but they would be covered by fresh hyaloclastite once the steam pressure escapes. I have visited tuya in Iceland and have observed the poorly consolidated nature of the hyaloclastite in the base of a tuya (but I cannot speak to the consolidation of material further up…these things are difficult to climb owing to their glassy particulate slopes. The cap is a result of the lava flows breaching the surface of the glacier and forms on top of the topmost hyaloclastite. It is always completely flat (as fluid basalt tends to produce flat flows (and sure, might have columnar cooling joints), and once it flows off of its hyaloclastite base and onto untouched ice, new explosions produce an effect similar to an Hawaiian ocean entry – ash, steam, and the general behavior we saw from Eyjafjallajokull this spring. the cap protects the hyaloclastite underneath it from erosion after the retreat of the glacier, but still the erosion happens as wind undercuts the basaltic cap and it breaks off.

Perhaps kilometers-thick continental ice sheets produce enough pressure to confound the explosive logic of ice meets lava, allowing for a more solid foundation, but to mention tuya without mentioning hyaloclastite clashes with what I know and have seen in Iceland. There is always variation with lava-type and geographic setting – I guess this type of landform could equally be called a tuya, although I don’t see this forming without such a significant weight of ice atop the volcano to allow for such a solid base. I learn something new every day!

@Lurking:
Thank you, made it much clearer.
It is then not either Herðubreiðartögl or Herðubreið that is unsettled. Instead it seems like there is a tube formation going on up to somewhere in between the two.
The data seems to correspond with 2000 and 2004 swarms. I think a fracturing would be more spread out in the north/south direction than this, here we can almost touch and see the tube forming.

Yeah… if that is what the quake stack means. I see these all over Iceland though. I wonder if it indicates activity in a localized area of the MAR (grinding, like on the San Andreas) or if it really is a tongue of magma snaking it’s way up to the surface. We know that at least some of these stacks are magma. (Eyj)

I don’t think that you are looking for work but if you provide a sequence of “Perspective Plot of Icelandic Quakes(s)” I can try and assemble the frames into an animated gif, or video if the gif is too large.

@Lurking #23 Amazing graphs! Thanks a lot! Looking at them it appears to me that Eyjaf-stack is far more “straight-to-the-point” if you get what I mean. I mean, there’s a difference, it’s more concentrated there, directly upwards, I don’t know if it is sign of anything…

@Gordon and.. pretty much every one else ref the plug-in idea. It can probably be done. On thing that I found handy was Nasa’s World Wind. Though a bit bulky, it allowed historical quakes to be plotted (provided you could find a working plugin) and the rendering was done by depth rather than on the surface. I wasted many CPU cycles fiddling with that. I think with Google Earth, the problem is going to be getting the surface to turn transparent so you can see the quakes at depth. That’s probably the biggest benefit of Nasa Worldwind; the ability to overlay different tile sets. (even ones that you accumulate locally if you have the drive space for it) Being solely built on the .net thing is a big distractor… almost as bad as being a java only applet. (CPU hog)

@Renato Rio: After a 8.8 EQ, you must be prepared for anything, anywhere. BTW, I felt this 6.5 (in fact I awoke), but none of the outer world (for me), but many people at the epicenter ran to the hills in case of a new tsunami. Later, about 8 more quakes of similar magnitude shaked the zone, but no injuries or damaged were reported.

@Guillermo: Thankfully nothing really bad happened to your people, but I can imagine the trauma that the memory of the big one left on them (I have some Brazilian friends who happened to be in Chile in February and they described it as a nightmare)..
BTW I was wondering if the Antofagasta tremors are linked to the after shock of that one, or if tremors in the region are considered to be from a different origin. There was also a strong one felt on that area yesterday.

The Antofagasta quakes are not aftershocks, but since it is expected a BIG EQ in the north of Chile, I’m afraid of these tremors could be the ‘introduction’ of the big one.
1-2 months before the 27F quake there was a lot of mid-intensity quakes in the epicenter of the future quake, so I’ll be watching the situation in the north.

#44 @Guillermo: I won’t ask for the impossible, because we all know it will happen (though I thought it would be further to the North). But I hope mother nature will spare Chilean people from another megathrust EQ in such a short interval of time. Chile responded bravely to February quake, so, let’s hope nature grants your people more time for recovery.